Lab 4 Worksheet 4-1 - Lab assignment from the online course PDF

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Lab assignment from the online course ...

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Group #:________________ People (please print names)_1._____________________ 2._________________ 3._______ 4._______ ___________ 5.______________________________ Lab 4: Diffraction and Interference of Light - Interference Pattern Created By a Diffraction Grating Warning: The laser beam is intense enough to burn the retina of your eye. Never look directly into a laser or let the laser beam shine directly or reflect into anyone’s eye. To complete this lab you will need the laser pointer, the diffraction grating with lines of known separation and the binder clips provided in your lab kit. The laser pointer is powered by 3 small batteries, do not keep it on for a long time or you will drain the batteries and the laser spot will not be bright enough to perform the experiment. In addition you will need a metric ruler or a meter stick, several blank sheets of white paper and tape. PROCEDURE 1. A diffraction grating consists of a large number of parallel, closely spaced slits. The number of lines/mm is indicated on the diffraction grating. Determine the distance between the slits (d) in m. d= 2x10-6 m 2. Tape a blank sheet of white paper to the wall. 3. Lay the meter stick or ruler on a table or the floor so the 0 meets the wall. 4. Use a binder clip to hold the diffraction grating and position the grating parallel with the wall. 5. Measure the distance between the diffraction grating and the wall (L) 6. Turn the laser on. Use the binder clip to maintain the laser pointer in the ON position. Use the second binder clip to keep the laser pointer level with the floor or table. In the picture below you can see our experimental set-up. m=1 First order maxima Central Maxima

L 1

7. Turn off the lights in the room. Direct the laser beam through the diffraction grating. Make sure the grating is perpendicular to the laser beam; measurements are not very accurate if the maxima are not centered on the central maximum. 8. You will be able to see the central maximum a pencil or pen to mark the central maximum maxima on either side.

nd the second order maxima. Use ot in middle) and the first order

9. With your phone take pictures of you exper did of ours. 10. Remove the paper and use your ruler to measure the distance between the central and the first order maxima on either side (x). Average the two distances. 11. After you have done one measurement, share your results with the other member of the group. Together, decide on six different lengths along the meter stick for which you want to perform the measurements. Record your values. Calculate the wave length of the laser beam: 12. First determine the angle θ (shown in the diagram) θ = tan-1(x/L).

13. Use the equation for constructive interference of a diffraction grating: d sinθ= m λ to calculate the wavelength of the laser beam produced by the laser pointer. In this equation, λ is the wavelength (in m), d is the distance (also in m) between lines on the diffraction grating, θ is the angle shown in the diagram and m is the order of the maxima. For each measurement, you need to first determine the angle θ then calculate sin θ and then determine the wavelength. Record your values for the wavelength, calculate your average measured wavelength. This is your experimental wavelength. Compare your value to the accepted wavelength provided by the manufacturer of the laser (you can read it on the laser pointer). You may use a table like the one bellow for your individual results. For this lab report, however, you need to share your results with the other members of your group and agree on the values that you want to enter in the table.

2

L (m)

x (m)

θ = tan-1(x/L)

λmanufacturer = 632.8 nm

1. .101m

.0355m

19.370

0.332

λexperimental (nm) 664nm

2. .15m

.0515m

18.950

0.325

650nm

650 nm  10

3. .20m

.07m

19.290

0.330

660nm

650 nm  10

4.

.086m

18.980

0.325

650nm

650 nm  10

5. .30m

.1045m

19.205

0.329

658nm

650 nm  10

6. .35m

.12025m

18.96

0.325

650nm

650 nm  10

.25m

sinθ

650 nm  10

14. Fill out the following table with the experimental results obtained by each member of the group: Name 1

λexperimental 655.33nm

% difference 0.82%

2

658 nm

1.231 %

3

675 nm

3.846 %

4

662 nm

1.846 %

5

|λexperimental - λ manufacturer| ×100 % Difference= λ manufacturer Does the experimental value of the wavelength you have determined agree with the accepted wavelength provided by the manufacturer of the laser? Explain. - Yes, the experimental value of the wavelength agrees with the accepted wavelength. The manufacturer wavelength is 650nm and the experimental average wavelength was determined to be 650.22nm. This is a 0.82% difference, which is extremely low, indicating that the two values are identical.

Each group member should insert pictures of their experiment here: 3

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5

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